The adrenergic nervous system and adrenal medulla play vital roles in maintenance of normal physiological functioning, and both types of tissue display similar characteristics on the biochemical and functional levels and in effects of drugs. In the neonatal rat, these tissues are markedly immature in their capabilities to synthesize, store and secrete catecholamines; it is commonly observed that many drugs which directly or reflexly alter catecholamine disposition in adults have markedly different effects in the immature organism, and that administration of these agents often produces permanent alterations in adrenergic function. The proposed study will examine the acute and chronic actions of several drugs to which fetuses or neonates may be exposed via clinical treatment or maternal self-administration (nicotine, reserpine, guanethidine) in adult rats and immature rats. The effects of drug exposure in utero and early in postnatal development will be contrasted with the actions in mature rats, and in addition the post-exposure developmental characteristics of catecholamine disposition will be evaluated for each drug.